138 BACTERIA. 



and more stable compounds is utilized in the presence of 

 animal and vegetable protoplasm in building up higher and 

 more stable materials ; though at the later stages of decom- 

 position these become fewer in number, and eventually 

 become oxidized into the more stable forms a free access of 

 air to the products of anaerobic decomposition always leading 

 to their oxidation. Hydration almost invariably occurs 

 during each of these stages. 



Schiitzenberger says, "Nothing resembles putrid fermentation, with 

 reference to the derived products, more nearly than the change which takes 

 place in the constituent parts of yeast, when left to itself without nourish- 

 ment, deprived of sugar and oxygen. 



We see, in fact, the appearance of leucine, tyrosine, sarcine, &c. 

 This is the first step ; the action stops there, and goes no further ; the 

 yeast, or the special soluble ferment which it secretes, is unfit to attack 

 these bodies again ; but if we wait for the development of vibrios, we 

 shall find the production of ammonia, carbon dioxide, and volatile fatty 

 acids at the same time that the leucine partly disappears." 



Fermentation by oxidation can only be set up by organisms 

 in the presence of a free supply of oxygen, and the process in 

 such cases appears to be due to special organisms which, 

 attacking the substance to be fermented, remove some of its 

 constituents, set free others, especially carbon and hydrogen, 

 which, in their nascent condition, are seized upon by the 

 oxygen of the air, and so water, or water and carbonic gas, 

 are formed. 



In the commonest of these fermentations by oxidation, 

 the acetic fermentation of alcohol, the free access of air is 

 as absolutely essential for the growth of the organism as 

 it is for the special stage of the fermentation of the alcohol 

 into acetic acid. 



If the mycoderma aceti be sowed in wine, freel} 7 exposed 

 to the air at a temperature from 24 to 27 C., chemists hold 

 that there is hydration of alcohol by the combination of an 

 atom of free oxygen with two atoms of its hydrogen water, OH 2 

 and aldehyde C 2 H 4 O, being formed, the latter of which, by 

 further oxidation, in turn becoming converted into, C 2 H 4 O 2 , 

 acetic acid. At a certain stage this process of acidification 

 stops, owing to the quantity of acid developed, but if this be 

 removed and fresh alcohol be added, the acidification again 

 commences, and so on, as long as the mycoderma remains 

 active, can obtain sufficient oxygen, and sufficient alcohol 



